柴达木盆地北缘大柴旦地区古生代花岗岩锆石SHRIMP定年   总被引：15，自引：2，他引：15  

吴才来郜源红  吴锁平陈其龙 Joseph L. WOODEN Frank K．MAZADAB Chris MATTINSON 《岩石学报》2007,23(8):1861-1875

大柴旦地区是柴北缘古生代超高压带的重要组成部分,与超高压岩石相伴的花岗岩十分发育。这些花岗岩具有两类不同的岩石地球化学特征,Ⅰ类以 Na_2O/K_2O 比值小于1、明显的负 Eu 异常和低 Sr、高 Y 为特征,具有 S-型花岗岩的属性,Ⅱ类以 Na_2O/K_2O 比值大于1、弱负 Eu 异常到正 Eu 异常和高 Sr、低 Y 为特征,具有Ⅰ-型花岗岩的属性,反映了它们的源岩及成因上的差异。锆石 SHRIMP U—Ph 定年结果表明,大柴旦地区花岗岩的年龄可分为三组,第一组年龄为446.3±3.9Ma,第二组年龄分别为408.6±4.4Ma、403.3±3.8Ma、401.8±3Ma,第三组年龄分别为374.5±1.6Ma、372±2.1Ma。结合区域地质特征,我们认为,第一组年龄可能反映了柴达木陆块与中南祁连板块碰撞的时代,第二组年龄可能反映了深俯冲地下的板块由于拆沉而折返的时代,第三组年龄可能反映了碰撞隆起后造山带上不同块体之间的伸展、滑塌的时代。  相似文献   

Assembling Proterozoic Australia: Inside out or outside in?     

Chris Clark  David E. Kelsey  Martin Hand 《Gondwana Research》2007,11(4):575-576

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Extraction of rhyolitic component of Vedde microtephra from minerogenic lake sediments   总被引：5，自引：0，他引：5  

Chris S. M. Turney 《Journal of Paleolimnology》1998,19(2):199-206

A technique is described for the extraction of rhyolitic microtephra from inorganic Lateglacial lake sediments. This technique was successfully applied by Lowe and Turney (1996) and is an adaption of the method described by Pilcher & Hall (1992) for application to Holocene peat deposits. It uses a density separation procedure to concentrate any microtephra component in lake sediments and was applied to the investigation of a lake sediment succession from a small basin in NE Scotland. Using this approach is was possible to define quantitatively for the first time the presence of the Vedde Ash tephra layer on the British Isles.  相似文献   

Geometric constraints on composition of sediment derived from erosional landscapes     

Chris Paola  & John B. Swenson 《Basin Research》1998,10(1):37-47

Although unroofing sequences are well known in the stratigraphic record, there is no general theory for estimating relevant basic quantities such as the time history of sediment production from a particular unit or the degree of mixing between successive units. Here we investigate the production of sediment from layered source rocks that are milled off by steady-state erosional topography. The shape of the sediment-production function for milling off a thin horizontal layer is given by the derivative of the hypsometric function, in the form of area contained within contours as a function of contour altitude. The time-scale for the production function, the ‘topographic mixing time’, is set by the topographic relief divided by the uplift rate. The production function for a sharp transition from one unit to another is given directly by the hypsometric function. The effects of stratal dip parallel to the mean slope of the erosional topography and finite layer thickness can be accounted for to a first approximation by simple geometric corrections to the mixing time. Finite layer thickness also has the effect of smoothing the production function although most natural hypsometric functions are smooth enough that this effect is relatively weak. The quality of an unroofing sequence can be measured in terms of the ‘sharpness’ of separation of successive peaks in sediment production produced by milling off a sequence of geometrically similar layers. This peak sharpness can be parameterized by a ratio of the interval between successive peaks in sediment production to topographic mixing time. By this measure, the quality of unroofing sequences is controlled by two parameters: the ratio of layer thickness to topographic relief, and the dip angle. The dip angle in concert with topographic mixing exerts a strong control on the degree of signal segregation; in particular, production of cleanly segregated signals for dip angles greater than about 15° requires very high ratios of layer thickness to relief. Hence identification of distinct unroofing sequences may place significant and useful constraints on the attitude and/or thickness of units in the eroding stratigraphy.  相似文献   

Improved ocean-geoid resolution from retracked ERS-1 satellite altimeter waveforms   总被引：6，自引：0，他引：6  

Stefan Maus  Chris M. Green  & J. Derek Fairhead 《Geophysical Journal International》1998,134(1):243-253

The ocean geoid can be inferred from the topography of the mean sea surface. Satellite altimeters transmit radar pulses and determine the return traveltime to measure sea-surface height. The ERS-1 altimeter stacks 51 consecutive radar reflections on board the satellite to a single waveform. Tracking the time shift of the waveform gives an estimate of the distance to the sea surface. We retrack the ERS-1 radar traveltimes using a model that is focused on the leading edge of the waveforms. While earlier methods regarded adjacent waveforms as independent statistical events, we invert a whole sequence of waveforms simultaneously for a spline geoid solution. Smoothness is controlled by spectral constraints on the spline coefficients. Our geoid solutions have an average spectral density equal to the expected power spectrum of the true geoid. The coherence of repeat track solutions indicates a spatial resolution of 31  km, as compared to 41  km resolution for the ERS-1 Ocean Product. While the resolution of the latter deteriorates to 47  km for wave heights above 2  m, our geoid solution maintains its resolution of 31  km for rough sea. Retracking altimeter waveform data and constraining the solution by a spectral model leads to a realistic geoid solution with significantly improved along-track resolution.  相似文献   

A Note on Extension Variances in IR2     

Chadœuf  Joël  Moran  Chris  Goulard  Michel 《Mathematical Geosciences》1998,30(6):575-587

Matheron (1971) proposed an approximation of the extension variance in IR. We propose in this note an extension of this formula in IR ² , based on a MacLaurin formula. Its application is shown in an example, the estimation of the maximum depressional storage of a soil surface.  相似文献   

A new look at the isotropy of narrow-line emission in extragalactic radio sources     

Chris Simpson 《Monthly notices of the Royal Astronomical Society》1998,297(2):L39-L43

We undertake a quantitative investigation, using Monte Carlo simulations, of the amount by which quasars are expected to exceed radio galaxies in optical luminosity in the context of the 'receding torus' model. We compare these simulations with the known behaviour of the [O  III ] λ5007 and [O  II ] λ3727 emission lines and conclude that [O  III ] is the better indicator of the strength of the underlying non-stellar continuum.  相似文献   

Discussion of Papers     

Chris Neuzil Discussion Editor   《Ground water》1998,36(4):547-547

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Introduction to modeling convection in planets and stars     

Chris Jones 《地球物理与天体物理流体动力学》2015,109(2):199-202

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Fitting sinusoids to observations of rotating spotted stars     

Chris Koen 《Monthly notices of the Royal Astronomical Society》2007,376(1):233-247

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